#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int i=0, flag=1;
	float sum=0;
	for (i = 1; i <= 100; i++)
	{
		if (i % 2 == 0)
			flag = -1;
		else 
			flag = 1;
		sum = 1.0 / i * flag + sum;

	}
	printf("%f\n", sum);


	return 0;
}